The goal of the study is to prevent spontaneous tumorigenesis and inhibit metastasis by active vaccination without inducing excessive untoward autoimmunity. With host tolerance to most tumor- associated antigens, efficacy of cancer vaccines can be expected only when administered in an environment with reduced negative regulation and enriched stimulatory signals. We demonstrated enhanced activity of Her-2/neu DNA vaccine after CD25+ regulatory T cell (Treg) depletion, but with concurrent induction of autoimmune thyroiditis. To obtain lasting therapeutic efficacy, thereby inhibiting subsequent spontaneous tumorigenesis and metastasis, further enhancement of tumor immunity will be required. Augmenting immune response may be achieved by providing appropriate costimulatory signals. In reported clinical trials testing peptide vaccine combined with a-CTLA-4 mAb, significant clinical response was accompanied by very severe autoimmune symptoms. The challenge is how to tilt the balance in immunotherapy and autoimmunity. We will test the benefit versus autoimmune risk of DNA vaccination combined with Treg depletion and immune modulation using CTLA-4 antagonistic Ab or CD137 agonistic Ab in our novel mouse model, i.e. rat neu transgenic BALB NeuT (NeuT) versus NeuTxDR3 mice with low and high susceptibility to experimental autoimmune thyroiditis (EAT) as determined by their MHC class II. Inhibition of spontaneous tumorigenesis and metastasis will be measured and the development of EAT and autoimmune gastritis will be the indicators of untoward autoimmunity. With the goal of tilting the balance toward tumor immunity, an additional focus will be on immune priming at the tumor site, while minimizing systemic immune modulation. We will test the hypothesis that the immunogenicity of a growing tumor can be amplified by in vivo transfection of the tumor cells with DNA encoding a foreign antigen, Tetanus toxin fragment C (TetC), delivered via nanoparticles. Specifically, we will 1. Measure tumor immunity and autoimmunity induced by neu DNA vaccination combined with CD25+ Treg depletion and exogenous costimulatory signals, 2. Establish a vaccination regimen to inhibit spontaneous tumorigenesis and tumor metastasis, and 3. Amplify the immunogenicity of a growing tumor by in situ transfection with TetC DNA.